1. Field of the Invention
The present invention relates to a liquid ejection head, a method of manufacturing same, and an image forming apparatus, and more particularly, to a liquid ejection head, method of manufacturing same, and an image forming apparatus, whereby liquid is ejected from ejection ports by changing the volume of pressure chambers connected to the ejection ports.
2. Description of the Related Art
An image forming apparatus is known which forms images on a recording medium, such as paper, by ejecting ink from nozzles toward the recording medium, while moving an ink ejection head having an arrangement of a plurality of nozzles and the recording medium, relatively to each other.
A known ink ejection head mounted in an image forming apparatus of this kind is a piezo type ink ejection head, in which ink is supplied to pressure chambers connected to nozzles, and the volume of the pressure chambers is changed, thereby causing the ink inside the pressure chambers to be ejected from the nozzles, by applying a drive signal corresponding to the image data to piezoelectric elements which are installed through a diaphragm plate on the outer side of the pressure chambers.
On the other hand, an ink ejection head fitted with unimorph type piezoelectric elements is also known, in which a portion of the inner walls of the pressure chambers (individual liquid chambers) is formed by a vibrating unit having a diaphragm, and piezoelectric elements are disposed on the side of this vibrating unit that is adjacent to the pressure chambers (see Japanese Patent Application Publication No. 2004-237676). Japanese Patent Application Publication No. 2004-237676 also describes setting the thickness of the diaphragm by means of the SOI (silicon on insulator) layer thickness of the SOI substrate, in order to ensure that the diaphragm has an accurate thickness.
However, as shown in FIG. 10, in an ink ejection head according to the related art, the upper surface and side faces of the piezoelectric element 60, apart from the fixing surface (bottom surface) where it is fixed to the diaphragm 56, make contact with the liquid inside the pressure chamber 52, through a passivation film (protective film) 964 having ink resisting properties, and the like. Therefore, the change in the volume of the pressure chamber 52 induced by the movement 91 of the upper surface of the piezoelectric element 60 and the change in the volume of the pressure chamber 52 induced by the movement 92 of the side faces of the piezoelectric element 60 counteract each other, and the volume of the pressure chamber 52 cannot be made to change efficiently with respect to the voltage applied to the piezoelectric element 60. Therefore, a problem arises in that ink cannot be ejected from the nozzle 51 with good efficiency.